1. Field of the Invention
The present invention relates to information recording/reproducing techniques for recording/reproducing information to/from an information recording medium, and more particularly to information recording/reproducing techniques capable of optimizing light radiation power to be used for recording information on the information recording medium, in accordance with the state of the recording medium.
2. Description of the Related Art
Optical disks and the like have already been used practically for recording/reproducing information by using laser beams. One example of rewritable optical disks is a phase change type optical disk which utilizes a reversible phase change between a crystalline state and an amorphous state. In order to obtain the amorphous state, an optical disk is heated to a melting point or higher by applying a high power (record power) and thereafter it is rapidly cooled, and in order to obtain the crystalline state, the optical disk is heated to a crystallization temperature by applying a middle power (erase power) between the high power and a read power and thereafter it is rapidly cooled. By changing the laser power in the above manner, information can be overwritten with a single laser beam. A method of setting an optimum record power when information is written upon radiation of a laser beam, is described in JP-A-7-73466 as a trial write recording control method. With this method, an optimum combination of the record power (high level) and erase power (middle power) for overwrite is decided in the following manner. Information is recorded with a record power having a constant ratio to an erase power, and by lowering the record power, the power level at which an erroneous operation during reproduction starts is detected. By changing the ratio to an erase power, the above operation is repeated. The smallest ratio of the record power to the erase power is obtained, and an operation margin is multiplied by the smallest ratio to determined the optimum record power.